When it comes to air filters, furnace filters, AC filters, and air conditioning filters, they are all labeled with three-part dimensions. The first number is the length, the second is the width, and the third is the depth or thickness. Let's take a look at the most common oven filter sizes and where to buy them. When ordering new air filters, it's important to round the measurements to the nearest whole number.
If your HVAC system uses a whole-house filter (which is usually located near the central furnace or air conditioning unit), you'll likely see a model number instead of the dimensions. For example, the Lennox filter below has part number X0583 and Honeywell part numbers FC100A1029 and FC35A1001, which can be replaced by this filter (see Lennox filter image below with item number and filter size along with compatible filters). It's important to check the actual size (the actual measured dimensions of the filter) to make sure you have the right one. Changing your HVAC filter is only one part of routine maintenance for your system.
If the filter is too small, it won't be able to trap all of the air and debris that passes through it. Cheaper fiberglass flat filters may need to be replaced every 30 days and may even be labeled as 30-day filters. If you use a room air purifier and need to replace the filter, it's essential to find the right size replacement HEPA filter. However, if you install a filter frame of incorrect size, it can cause air leaks which significantly reduces its effectiveness.
This rounded measurement is known as the nominal size and is used to match the right air filter to its corresponding groove. Filters can have a list of models from various manufacturers that are compatible with what you need.
